Method and apparatus for producing vacuums



K. c. D. HICKMAN ETAL 2,379,436

METHOD AND APPARATUS FOR PRODUCING VACUUM Filed May 20, 1942 4Sheets-Sheet 1 July 3, 1945.

FIG.. 1.

FINE VACUUM FORE v VACUUM KENNETHCDHICKMAN GEORGE A.KUIPERS' INVENTORS53m bH Hum y 1945- K. c. D. HICKMAN ETAL 2,379,436

METHOD AND APPARATUS FOR PRODUCING VACUUM Filed May 20, 1942 4Sheets-Sheet 2 A B c FORE VACUUM VACUUM IZA T Z -125 42c 41 f 5 41A -mFINE A B C VACUUM VACUUM 7 '75 54 21s 2|c- ZIA m a J at at x 40 10A \53IOC/ 5| 55 q E 1L 1 J J 47 E43 KENNETH C.D.HICKMAN GEORGE A.KUIPERSINVENTORS %//2MM BY -rum ATTORNEY 23;); GAS PUMVS ANU ml, 13;, ,1: :3130% J y 1945- K. c. D. HICKMAN ETAL ,379,436

METHOD AND APPARATUS FOR PRODUCING VACUUM Filed May 20, 1942 4Sheets-Sheet 3 FIG. 4

KENNETH C.D.HICKMAN GEORGE A .KUIPERS INVENTORS ATTORNEY July 3, 1945.

K. C. D. HICKMAN EI'AL METHOD AND APPARATUS FOR PRODUCING VACUUM FiledMay 20. 1942 4 Sheets-Sheet 4 no FIG.5

E 109 m I a ,los 90 1 l06 5 9? 1 4 ;i i! i! E! KENNETH C.D.HICKMANGEORGE A.KUIPERS INVENTORS W kl/h aw BY W ATTORNEY Patented July 3, 1945UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR PRODUCING VACUU'MSKenneth C. D. Hickman and George A. Kuipers,

Rochester, N. Y., assignors to Distillation Products, Inc., Rochester,N. Y., a corporation of Delaware Application May 20, 1942, Serial No.443,732

25 Claims.

This invention relates to a method of producing vacuums and to vacuumpump apparatus for practicing said method.

Among the fluid actuated pumps, those of the steam or water ejector typeand of the condensation type are more commonly used in the production ofvacuums on an industrial scale.

Of these types, the ejector pump has been very effective down to a limitcorresponding with the saturation pressure of water at out-doortemperatures which will range from just above freezing to about 30 C.and corresponding with vacuums of about mm. to 40 mm. of mercury.Consequently, vacuum pumps of this type have been limited in their rangeof practical operation to a lower limit of vacuum pressures of 5 tomillimeters of mercury. This condition arises from the fact that theefliciency of a steam or water ejector drops away very rapidly at thelower limit of its range. The rapid decline in the efliciency of theejector pump at lower pressures, arises from the behavior of themolecules of vapor issuing from the male jet. According to theMaxwellian distribution of thermal velocity, there are always a fewmolecules which have a greater random velocity than the issuing vaporjet or stream and these molecules, together with others that haveaccidentally hit projections of the ejector, return against the stream.These returning molecules become part of the load and greatly cut downthe efliciency of the ejector as mentioned.

The inefliciency of the steam or water ejector at low intake pressuresbecomes especially marked when the pump is withdrawing water vapor, asin the case of the evaporation of' foods or the drying of textiles orother industrial products. Under those conditions, the ratio between theactuating steam and the load is disappointingly low, since, for everyunit of load, the intercondenser oi the pump system must handle from 10to 1000 times as much actuating steam, depending on the lowness of thefine pressure desired. Aside from the expense of operating such a pump,due to the amount of steam and cooling water required, there is theadditional disadvantage that each pump is very bulky and a great many ofthem would be required in any given dehydrating installation.Furthermore, this type of pump is limited to use in those locationswhere a large supply of steam and a plentiful supply of cooling waterare available. Thus, they would be ill-adapted to form a part ofportable apparatus such as would be needed in equipment designed to betaken into the fields for the dehydration of fruit, vegetables and thelike.

The condensation type of pump, on the other hand, readily developsvacuums, in the range between .1 of a millimeter down to 10- or less,but it has a very limited capacity and, therefore, is ill-adapted foruse where large volumes of gases must be evacuated. In the condensationpump using a stable organic fluid, no attempt has been made toaccelerate the issuing molecules to speeds above the random thermalvelocity of the majority of the particles being evacuated. Instead, agentle stream of vapor is generated and thrust towards the difluser andall molecules of working fluid which tend to return against the streamare condensed by adjacent cold surfaces. Here the limiting vacuum isdirectly related to the vapor pressure of the pump fluid at thetemperature of the cold condensing surfaces.

From the foregoing explanation, it will be appreciated that theabove-mentioned fluid-actuated types of pump have been impractical inthe range between 6 mm. and .1 mm., that is, in the range between thelower limit of the ejector pump and the upper limit of the diffusionpump. Thus, these two types of pumps leave a gap in the vacuum spectrum"which neither has been able to fill with practical or commercialsuccess.

The high velocity mercury ejector as developed by Parsons is capable ofeffecting evacuation throughout the desired low pressure range. However,the actuating fluid of the Parsons ejector is mercury which breaks upinto droplets diflicult to collect since they wander into every nook andcranny of the apparatus. The resulting mercury vapor is highlyobjectionable since it is poisonous and requires a liquid air trap toprevent it from passing into the chamber being evacuated. This mercurytype of pump is therefore unacceptable for dehydration uses, especiallyin the dehydration of 'foods.

The use of organic actuating fluids in condensation pumps has beenproposed where the prevailing boiler presurse therein is low and theactuating vapor issues from the jet as a gently flowing stream.

It has also been proposed, as in the patent to Lewis, 2,028,340, to usepetroleum fluids as the actuating mediums in ejector pumps, but thispatent points out that these fluids tend to de compose at high boilerpressures. Consequently, the petroleum actuating vapors disclosed inthat patent were not accelerated to a speed which for the most partexceeded the relatively great ran dom velocity of certain of the gasmolecules.

The main feature of the present invention relates to a novel method ofproducing high vacuums by forcing a stream of greatly acceleratedorganic fluid, in aspirating relation to a passage containing the gas tobe evacuated, all of which is effected without substantial decompositionof the organic fluid and without the interposition of a cooling trap.

A further feature of the invention relates to the provision of a novelvapor ejector pump system for practicing said method, which system willoperate in the range between substantially zero pressure, (10- or less)and including the range normally effective for a steam or water ejectorpump, namely above 6 millimeters, on the fine vacuum side of the pumpwhere a pressure of to or millimeters of mercury prevails on thefore-vacuum side. The pressure of the operating fluid used in the novelpump system is sufliciently in excess of the forepressure to operate thepump and cause water vapor aspirated by the pump to condense in thefore-vacuum at the temperature produced by the cooling water availableat the locality.

Another feature of the invention relates to a multi-unit ejector pump inwhich each unit thereof is operated by a different organic actuatingfluid fraction having characteristics best suited for that unit.

An additional feature of the invention relates to the provision in amulti-unit pump using different organic fractions, of apparatus thatwill automatically separate out from any mixtures of such organicfractions occurring in use, the original fractions and will return eachto its appropriate unit.

Still another feature of the invention relates to a novel jet anddiffuser arrangement whereby greatly improved results are obtained.

Other features and advantages will appear from the detailed descriptionand claims when taken with the drawings in which:

Fig. 1 is a front elevation, partially in section, of aseries-connected, multi-unit pump system in accordance with the presentinvention; and Fig.

la is a view of a straight type diffuser jet that can be substituted forone or more of the Venturi type diffuser jets in the system of Fig. 1;

Figs. 2 and 3 are diagrammatic showings of series-connected, multi-unitpump systems respectively provided with different forms of selfpurifyingapparatus for effecting automatic separation of and distribution of theseveral actuating fluid fractions to these respective units;

Fig. 4 is a side elevation, partially in section, of a multi-unit pumpsystem in which the units thereof are connected in parallel; and Fig. 4ais a vertical sectional detail view of a male jet used therein;

Fig. 5 is a view, partially in section, of a parallel-connectedmulti-unit pump system similar to that illustrated in Fig. 4 butdiffering therefrom in the vapor box and difluser jet manifoldconstruction as well as in the arrangement for affording selective zonalcooling for the diffuser jets; and

Fig. 6 is a diagram illustrating a series-parallel pump system wherein aplurality of parallel pump constructions of Figs. 4 or 5 can beconnected in series in accordance with the arrangements of Figs. 1 and3.

In Fig. 1 there is illustrated one form of the pump system of thepresent invention. This system comprises a plurality of pump units, A, Band C connected in series arrangement. Each pump unit such as A,includes a boiler IOA opening into conduit 1 IA which extends in sealedrelation through the wall of an air chamber HA. Within this chamber, theconduit communicates with a downwardly extending male jet IZA. Theboiler IDA contains a stable organic actuating fluid HA, the nature ofwhich will be hereinafter described.

The boiler may be heated by any suitable means but, as hereinillustrated, it is heated by a steam coil |5A having a section thereoflocated in the bottom of the boiler and another section thereof woundexternally about the lat eral walls of the boiler. This coil iscontinued as a section ISA enclosing the conduit I I so that the vaporgenerated from the fluid in the boiler will not cool in its travelthrough this conduit.

The male jet I2A opens into one end of a diffuser jet HA mounted so thatthe passages through said jets are in axial alinement. The mentioned endof the diffuser jet communicates with and is sealed to the lower wall ofan air chamber I3A which is connected to the fine vacuum pipe. Thediffuser jet, although the invention is not so limited, is preferably ofthe Venturi type having a zone d at the neck thereof including a portionjust preceding the area of impact therewith of the organic vapor issuingfrom the male jet. The diffuser jet also has a second zone e extendingfrom the first portion to the narrowest part of said jet and it is alsoprovided with a third zone I coextensive with the narrowest portionthereof. The diffuser jet further includes a fourth zone g coextensivewith the remaining flared portion thereof. Each of the zones of thediffuser jet are individually cooled by a water jacket 19A surroundingthis jet and communicating with a suitable water supply through thepipes 20A. Thus, the several zones can be selectively cooled to theprescribed temperature best suited for eflicient operation. It will beunderstood that the invention is not limited to cooling all four ofthese regions but also includes the arrangement where zone d only iscooled.

We have discovered that the diffuser jets of the Venturi type utilizedin the system of Fig. 1 may be replaced by a diffuser jet of the type,disclosed in Fig. 1a, provided with substantially straight side walls,defining a passage therethrough of uniform diameter.

The end of the diffuser jet communicates with a cylindrical condenser2iA sealed to the lower end of this jet. This condenser is cooled in anysuitable manner preferably by cooling water circulating through thecooling coils 22A located within the condenser adjacent its bottom andat the side walls thereof. The condenser opens into a pipe 23A having apump 24A therein for returning the condensed actuating fluid back to theboiler IOA.

The constructions of the pump units B and C are similar to that of unitA so that it will be unnecessary to describe them since in the drawings,the parts of units B and C corresponding to unit A, are designated bythe same reference numerals with the added suffixes B and Crespectively.

It should be mentioned that a conduit 26 having one end sealed in a sidewall of the condenser 2IA communicates with the air chamber I3B of thesecond pump unit B. Similarly, a conduit 21 connects the condenser 21Bof the pump unit B with the air chamber I30. Also, the condenser 2|Ccommunicates with the fore-vacuum pipe 28. It should also be pointed outthat the diameters of the male jet I23 and of the receiving jet I'IB aresmaller than the corresponding parts in the unit A and that thediameters of the male jet I20 and the receiving jet IIC are smaller thanthe corresponding jets of the pump unit B. In other words, the diametersof the male jets and of the receiving jets progressively decrease insize from the fine vacuum end of the pump system to the forevacuum endthereof.

The actuating fluids to be used in the boilers I0, I03 and C in the pumpsystem of Fig. 1 comprise stable organic fluids. While various fluidsmay be used, it has been discovered that for highest pump efilciency thefluids used should have certain definite characteristics. If the fluidis too volatile it may prevent the establishment of the proper vacuumand in borderline conditions may provide an aureole of partiallycondensed vapor around the male jet which limits the influx of the gasto be pumped. Furthermore, the vanor of a too volatile pump fluid may becarried away in minute amounts into the forevacuum. It will beappreciated that during the course of a short time of pump operation,the fluid will be revaporized and condensed thousands of times so thatthe accumulated loss into the forevacuum may be high and the boiler willsoon become empty.

When the boiler fluid is of lower volatility than the optimum, the finepressure may be excellent but the thermal eficiency sufi'ers. More heatmust be put into the oil and the temperature of the boiler rises undulywhich may cause weakening of the walls, starting of the seams anddisintegration of joints and vapor pipelines. When the condition becomesaggravated the temperature rises so high that polymerizing and gummingoccurs in the boiler, gaseous decomposition products are evolved and thevacuum is again impaired because of these uncondensibles. With suchfluids, it is customary to use lower boiler pressures in order toapproximate usual boiler temperatures and this in turn lowers thepermissible expansion ratio in the male jet and reduces the entrainmentratio.

In general, the vapor pressure of the fluid should be substantially lessthan the lowest pressure to be produced at the preferred temperature ofthe condenser and manifold surrounding the male jet. The vapor pressureof the pumping fluid should be so low that in the apparatus for which itis designed for service, the unrecoverable escape of fluids shall not begreater than, say, 50% in 24 hours.

Where food dehydration is concerned the liquid shall not be hydrolizableby water or water vapor under operating conditions. In general, thevapor shall not be harmfully reactive with the materials handled underthe chosen operating conditions.

By way of example, there follows a table of preferred characteristicsof, and sources of suitable actuating fluids for specified operatingconditions.

3m. L1! Home List of preferred boiling points and sources of actuatingfluids for specified operating conditions As source of the above oils wehave used:

AWinter grade crank case oil (WW) B-50 W white oil CLight processing oilDSpindle oil E-Ice machine oil F-Fuel oil No. 1

GFue1 oil No. 2

The actuating fluids for the boilers are not these oils but suitablefractions distilled from them to meet the vapor pressure-temperaturerelations specified. Other fluids meeting these requirements areconsidered within the scope of this invention. Where the systemcomprises three pump units connected in series, boiler IUA willpreferably utilize a mixture of fractions I and II, boiler IIIIBpreferably will use fractions III and IV, and boiler IOC will preferablyemploy fraction V.

In the operation of this multi-unit, series-connected pump system, theactuatin liquids in the boilers IOA, I03 and I00 are heated to convertthem into their vapor phases and to accelerate the flow of these vapors.In the case of the unit A, the actuating liquid in a boiler IDA isheated to a temperature preferably in the range from 200 to 250 C. at aboiler pressure of from 2 to 12 cm. Under these conditions, the liquidin this boiler is converted into a vapor which flows through the conduitHA and issues from the male jet l2a at a velocity greatly in excess ofthat ordinarily prevailing in a condensation pump. For example, thevelocity of the vapor issuing through the male jet I M is greater thanthe random thermal velocity of the majority of the molecules of the gasor vapor being evacuated. This accelerated stream of actuating vaporissues into the diffuser jet HA in aspirating relation to the passagefrom the fine vacuum pipe. The walls of this diffuser jet in thementioned regions 11, e. f and 9, thereof. are selectively cooled by theseveral water jackets to provide zonal cooling thereof, since the cooldiffuser walls substantially limit the flow of the molecules of theissuing vapor to a forward direction. In other words, the relativelyhigh velocity of the issuin vapor and the constricting action of thecool condenser walls thereon, insure that substantially a l Of themolecules of the vapor will continue along the principal direction ofthe vapor stream. From the difiuser, the vapor with the gas to beevacuated entrained therein, passes into the condenser 2|A. It should benoted especially that the diffuser jet opens directly into the condenserso that the actuating vapor is not required to pass through any conduitof restricted cross section which would greatly obstruct the forwardflow from the mentioned jet. It should also be pointed out that thecharacteristics of the actuating fluid are such that the vapor willcondense readily at the temperature of the usual water supply. From thecondenser, the pump 24A returns the condensate through the pip 23A tothe boiler IDA. The gas to be evacuated is advanced through the conduit26 to the pump unit B.

The actuating fluid in boiler I DB of this unit is preferably heated toa temperature of from 170 to 220 C. at a pressure of from 6 to 35 cm.The operation of the pump unit B is similar to that of the unit A exceptthat the vapor from the boiler IDB and the male jet I2B, issues at ahigher velocity than the vapor at unit A. In this instance also, thecondensate from the condenser ZIB is pumped back to the boiler IDB. Thegas to be evacuated is advanced from the condenser 2IB through conduit27 to the pump unit C.

Here again the evacuating operation is continued. In this instance,however, the fluid in the boiler is heated at a temperature of from 160to 250 C. at a boiler pressure of to '70 cm.

Under these boiler conditions, the vapor generated in the boiler IDC isgreatly accelerated and it issues from the male jet I2C at a velocitygreater than the acoustic velocity of sound in the actuating vapor. Herealso, the condensate formed in the condenser is pumped back to theboiler IDC for reuse. However, the gas to be evacuated, passes to thefore-vacuum pipe.

From the foregoing description, it will be appreciated that there isprovided, a novel method of producing vacuum, effective from atmosphericpressure to extremely low pressures, and yet the use of poisonous andotherwise objectionable actuating fluids, are avoided. In this method,there are utilized organic actuating fluids, preferably derived from thefractional distillation of certain petroleum products, the fluids beingheated so that the velocity of the resulting actuating vapors areaccelerated to a degree previously considered impossible without thermaldecomposition thereof. By using vapor jet velocities in excess of therandom thermal velocity of the majority of the vapor molecules and alsoin excess of the random motion of the gas being pumped, evacuation iseffected throughout the vacuum spectrum, even to the lowest pressuresordinarily sought in industrial processes.

It is a shortcoming of petroleum fluids that they are unlikely to behomogenous. Therefore, in order to avoid the presence of light fractionswhich impair the vacuum, it is necessary, as a practical matter, to useactuating fluids containing too many heavy fractions for the mosteconomical operation of the pump. Furthermore, the pump, duringoperation, is likely to become contaminated with material which has anafllnity for the pump fluid so that the composition of this fluid willbe altered thereby. In accordance with the present invention, it isproposed to provide a multi-stage or multi-unit pump system in whicheach stage is operated by a fraction most suitable therefor. It is alsoproposed to include self-purification apparatus in the pump system,which apparatus will automatically separate the various fractions fromany mixture of actuating fluids, and which will distribute each of theseparated fractions to the pump unit to which it is best suited. Thisresult may be achieved either by fractional condensation or byfractional distillation.

In Fig. 2 there is shown a modified evacuating system in which there isan arrangement for effecting fractional condensation of the actuatingfluids and for distributing each separated fraction to its appropriateboiler. This arrangement employs a plurality of pumping units A, B and Cconnected in series after the manner of the system shown in Fig. 1.However, the diffuser Jets I13 and IIC of the units B and C respectivelyare provided with gutters 35B and 35C at an intermediate point thereof.Each gutter is connected by a pipe 31 to the preceding boiler in theseries beginning with the forevacuum end of the system. Thus, the gutter35C of the diffuser jet I'IC communicates through the pipe 310 with theboiler IDB, similarly the gutter 35B of the diffuser jet I'IBcommunicates through the pipe 313 with the boiler IDA. It will be notedalso that the boilers IDA, IDB and IDC are located at diflerent levels,the elevation of each boiler being determined by the vapor pressure ofthe actuating fluid therein. Thus, since the vapor pressure of the fluidin the boiler A is less than that in boiler B and since the vaporpressure of the fluid in the boiler B is less than that in boiler C,boiler A will be at the highest elevation, boiler B at an intermediatelevel and boiler C at the lowest level. It will be noted that boiler IDAcommunicates with boiler IDB through a pipe 38A having a trap therein.

The operation of this modified system in effecting evacuation is thesame as that of Fig. 1 and need not be redescribed here. It should bepointed out, however, that the first fluid to condense in the gutter 35Cof the difluser jet IIC will be the highest boiling constituent of thevapor and this condensate is conducted through pipe 310 to boiler IDBwhere the fluid is again vaporized and sent to the male jet I2B. Theexcess condensate from the jet I'IC over and above that needed in theboiler IDB flows by gravity through pipe 383 to boiler IDC. Likewise,the actuating vapor issuing from the male jet I2B of pump unit B issubjected to partial condensation in the diffuser jet IIB wherein thehighest boiling fraction collects in gutter 353. From this gutter, thecondensate flows to boiler IDA where it is reboiled to provide actuatingvapor for its jet I2A. It will be understood that if there isinsuflicient fluid in the boilers IDA and IDB, this deficiency can bemade up by adding a cruder fraction of the actuating fluid to the boilerIDC from which the higher boiling fractions will pass as alreadydescribed to the respective boilers IDB and IDA in the order named.

In Fig. 3, there is illustrated another modified evacuating system inwhich there is provided means for effecting fractional distillation ofthe actuating fluids and for delivering each fraction to its properboiler. In this arrangement also the pump units A, B and C are connectedand operated in the manner previously set forth. However, there is alsoprovided a rectifying boiler 40 with a rectifying column 4I. This boileris provided with an inlet pipe 43 through which fresh oil iscontinuously available for this boiler as needed. The level of the oilin the boiler is determined by a level-controlled float valve 44 whichcontrols the opening and closing of the inlet pipe 43. The upper part ofthe rectifying column communicates with the forevacuum pipe and alsowith the pipe 45 from the condenser 2IC of the pump unit C so that anylighter fractions of vapor not condensed therein will condense in therectifying column. This column has a gutter 4IA therein in which theundesired lighter fractions collect and can be discharged through thepipe 46. The rectifying boiler 4D is connected at its bottom portionwith the boiler IDC, through the pipe 41. The flow of fluid through thepipe 41 is determined by a level-controlled float valve 48C located inthe boiler IIIC so that a uniform level of liquid is maintained in thisboiler. Similarly, the boiler NC is connected to the boiler IOB by apipe 49 governed by a level-controlled float valve 483 in the boiler IOBto maintain the desired liquid level therein by controlling theadmission of fluid through the pipe 49. In like manner the boiler IOBcommunicates through pipe 50 with the boiler IOA wherein there islikewise provided a level-controlled float 48A which also maintains apredetermined level in this boiler by controlling the flow of fluidthereto through the pipe 50. The bottom portion of the boiler IUAcommunicates through a pipe with the bottom portion of a purifyingboiler 53 for the nonvolatiles. The upper portion of this boiler orpurifier communicates through a conduit 54 with the upper portion orvapor chamber of the boiler A. while the bottom of the boiler 53 isprovided with a discharge pipe 55, the inlet to which is controlled by athermostatically operated valve 51. All of the mentioned boilers areprovided with heating means not illustrated. It will be understood thatthe float valves are shown by way of example only and that the leads maybe controlled by other well-known means.

The operation of the pump units A, B and C is similar to that alreadydescribed and need not be repeated except to mention again that theboiler NC is operated at the highest pressure. boiler IllB at anintermediate pressure and boiler 10A at the lowest pressure. Thesepressures are, of course, determined by the characteristics of thefractions of actuating fluid used. in accordance with the tablepreviously given. However, with the self-rectifying arrangement hereinprovided, oil including the fractions suitable for use in the boilersHJA. 10B and WC is available through pipe 43 so that the float valve 44maintains a given level of oil in the boiler 40. It is assumed that thelevel of the actuating oils or fluids in the remaining boilers is at thepredetermned point. However, if the level in the boiler IUC is abovethat required, its float valve 48C will open permitting fluid to flowfrom boiler I00 to boiler MB. This. of course. will disturb the level inthe boiler HJB which will open its float-controlled valve 483 so thatactuating fluid or oil can flow to boiler IDA. The level of the oil inboiler IDA will likewise be disturbed so that float valve 48A will openpermitting excess fluid to flow to boiler 53. Similarly fioat valve 44in boiler 40 wll operate to maintain the level in this boiler. It willbe understood that this restoration of the levels in the boilers 10A.IIJB and IOC will admit to each boiler, fractions of the fluid otherthan that best adapted for the operation of the particular pump unit inquestion. However, the li hter fractions will tend to flow from left toright "11 the system as illustrated, this flow taking place through acondenser unit or units until the fraction condenses into itsappropriate boiler. On t e other hand. the heavier fractions will flowfrt .n boiler to boiler, from right to left in the system until t enon-volatiles accumulate in the purifyin boiler 53. When an excess ofnonvolatiles accumulate in this purifying boiler, the temperature ofthese non-volatiles will rise to a point where thethermostatically-controlled valve 51 will open the discharge pipe 55 toperm t the excess to be discharged through this pipe. In thisarrangement, the actuating fluid is cleared of its undesired lightvolatiles and is also cleared of undesired non-volatiles while thesuitable fractions of the purified oil or actuating fluid are autobed:(Ti Knew matically distributed to their appropriate boilers inthesystem. This arrangement insures that each pump unit in the systemwill be operated at its highest efficiency.

A further modified form of the invention is shown in Figs. 4 and 4awherein the pump units or stages are connected in parallel instead ofbeing connected in series as in the arrangements de scribed above. Inthis modification there is likewise provided a closed boiler 66 adaptedto heat the actuating hydrocarbon fluid contained therein to apredetermined temperature. The top of this boiler communicates with aconduit 6| which extends upward and is then arched for communicationwith a connection nipple 63, attached to the circular cover plate 64 ofa diffuser jet manifold. This manifold. in addition to the mentionedcover plate. includes a circular bottom plate 65 of like diameter as thecover plate. The bottom plate has welded thereto, the lower edge of acylindrical casing 66 of slightly smaller diameter than that of thementioned plates. The upper end of this casing is welded in the openingof an annular ring 58 which serves as a fiange for connecting thiscasing to the cover plate by means of suitable clamping bolts. There ismounted within the manifold a diffuser jet assembly unit comprising thementioned bottom plate 65. The unit also includes a second cylindricalcasing 69 substantially shorter than and of smaller diameter than thefirst casing 66. This second casing has its lower edge welded to thebottom plate in coaxial relation with said first casing, while its upperedge is welded to the periphery of a, top plate 10. The mentioned topand bottom plates have alined openings therein. In each pair of thesealined openings, there is mounted a diffuser jet II of the Venturi typewith the top and bottom ends of each such jet secured in the mentionedalined apertures by being welded to the respective top and bottomplates. The diffuser jet unit is thus arranged so that cooling water orother fluid can be circulated, by means not shown, through the unit incontact with the outside surface of the diffuser jets without leakinginto the actuating fluid which passes through these jets. It will beunderstood that the several diffuser jets may be provided with zonalcooling, as disclosed in Fig. 1. A fine vacuum pipe 13 communicates withthe space inside of the diffuser jet manifold.

It has been mentioned that the boiler communicates through the conduitwith the connection nipple 63 on the cover plate 64 of the manifoldassembly. This connection nipple opens into a vapor chamber formed bywelding the rim of a cup 14 to the underside of the top plate, the cupbeing approximately of the same diameter as that of the second casing 69and arranged coaxially therewith. The bottom of the mentioned cup isprovided with a number of apertures equal in number and arranged inalinement with the openings in the top plate. In each of the theseapertures in the cup bottom, there is screwed a flaring male jet 15(Fig. 4a.) with its lower end preferably extending into the upper end ofone of the receiving jets. It will be noted that the upper end of eachof the male jets projects well above the bottom of the mentioned cup.However, a pipe 12 with a liquid trap therein, communicates with thebottom of the cup so that if any of the actuating vapor condenses in thevapor box, this condensate will be discharged therethrough to the hotcondenser. Inasmuch as the upper ends of the male jets project wellabove the bottom of the vapor box,

the condensate cannot enter therein to clog them but instead the jetswill remain dry thereby insuring the most efficient operation of thepump.

It should be particularly pointed out that the walls of the vapor boxare so positioned that there is an extremely long metallic path betweenthe male jets and the diffuser jets H. Furthermore the walls of thevapor box are covered with heat insulating material 16 to preventthermal losses. Additional provisions against such thermal losses maycomprise supplying the walls of the vapor box with additional heat suchas by heating coils (not shown) an by polishing or mirroring of theoutside surface 18 of each of the male jets.

The bottom plate of the diffuser manifold has clamped thereto, the upperend of a hot condenser. This hot condenser comprises a verticallyextending cylindrical pipe 8| provided with a flaring portion 82 andhaving its upper end of a diameter substantially equal to the diameterof the inner casing of the diffuser jet assembly. The upper edge of thisflaring portion is welded in a ring 84 which serves as a flange to beclamped by suitable clamping bolts to the bottom plate of the manifold.A suitable gasket interposed between these parts seals them together.The lower end of the hot condenser opens into a cylindrical, horizontalreservoir 85. Preferably, the lower end of the cylindrical pipe and theleft end of the boiler are mitered and welded together in accordancewith the usual elbow construction. Likewise, the right end of thereservoir has joined thereto the vertical chimney 86 of a cold condenserunit, the chimney and reservoir being likewise joined together by thementioned elbow construction. The chimney at a point just above the topof the reservoir has welded therein a horizontal ring 81 with anintegral upstanding flange which provides a suitable gutter for thecollection of condensate formed on the inner wall of the chimney. Thisgutter is provided with a discharge conduit 88 which may be connected inparallel with a discharge conduit 89 provided at the bottom of thereservoir. The upper end of the mentioned chimney is welded to a ring 90providing a, connection flange, adapted to be clamped to an annularcover plate 9|, the ring having an opening therein of a diametersubstantially smaller than the diameter of the mentioned chimney. A tube92 of approximately the diameter of this opening is welded to theunderside of the cover plate 9| to communicate with said opening. Thementioned tube is slightly shorter than the chimney and its lower end isclosed by a circulate plate 93 formed with an upstanding outer flange toprovide a gutter at the lower end of the tube. This gutter collectscondensate forming on the outside or the outer wall of the tube 92, andis provided with a discharge conduit 94 opening into the first mentionedgutter. The tube near its upper end is provided with an aperture 95 sothat the annular flue between the chimney and the tube communicates withthe opening in the cover plate, which opening leads into the fore-vacuumconduit 96. The mentioned annular flue space is provided with a coolingcoil 91 for the cir- ,culation of cooling medium therethrough, cerin ofthe turns of this coil contacting the outer wall of this tube and otherturns thereof contacting the inner wall of the chimney so that both thechimney and the tube will serve to condense the vapors.

It has been mentioned that the condensate from the cold condenser aswell as from the hot condenser and the reservoir are discharged intoconduits 88 and 89 which lead to the common pipe 98 and thence into thetop of the oil separator 99. This separator comprises the usualreceptacle provided at a point spaced from the top thereof with an oiloutlet pipe I00 leading to a gear pump IOI which advances the oil backinto the boiler 60. The bottom of the oil separator is provided with apipe I92 through which water is discharged. This pipe is provided with ariser that extends to a point I03 just slightly below the oil dischargepipe.

In the operation of this parallel connected multi-unit pump system, theboiler 60 is heated to vaporize the actuating fluid therein. Thisactuating fluid preferably has the characteristics of the fluiddesignated IV in the mentioned table. Consequently, the fluid in theboiler will be heated to a temperature in the range from to 220 C. at aboiler pressure of 10 to 35 cm. With the boiler heated to the mentionedtemperature, the vapor or actuating fluid will be accelerated so that itissues through the male jets 15 at a velocity greater than the randomthermal velocity of the gas being pumped. The accelerated vapor issuingfrom each male jet streams into its related diffuser jet H and in sodoing, entrains some of the gas to be evacuated. The wall of eachdiffuser jet is cooled by zones as in Fig. 1 or uniformly throughout themajor portion of its length, with the result that these cooled wallswill reduce the tendency of the vapor molecules to diverge therebyinsuring that substantially all of the vapor stream will continue toflow along the principal direction of movement of the stream. Thisrestriction of the divergence of the molecules of the vapor streamtogether with the high velocity at which the stream issues from the malejet, assures substantially n0 retrograde flow of any part of theactuating vapor. As a result of this condition, the present ejector typeof pump functions with remarkable efficiency even in the low pressurerange usually restricted to condensation and mercury actuated pumps.

After passing through the diffuser jets, the actuating vapor withevacuated gas entrained therein flows into the hot condenser 8| whereinsome of the vapor is condensed and collects in the reservoir 95. Theuncondensed portion of the vapor as well as the entrained gas passesinto the cool condenser wherein the remainder of the vapor is condensed,the gas, of course, passing out of the cold condenser into theforevacuum conduit 96. The vapor condensate accumulating in thereservoir and the cold condenser flows to the oil separator 98 where theoil is separated from the water therein. The oil in the top portion ofthe separator is returned oy the gear pump Illl to the boiler 60, the waer in the bottom of the separator, of course, flows through the pipe I82to a suitable drain. By employing the hot condenser, the major portionof the actuating fluid is condensed at relatively high temperature sothat it can be returned to the boiler with a minimum loss of heat.However, the cold condenser is necessary to recover the remainder of thefluid at a lower temperature with somewhat more dissipation of heat.Nevertheless, this condenser arrangement efiects a substantialimprovement in thermal efliciency.

In Fig. there is illustrated a further modified form of pump system inwhich the several pump units or stages are connected in parallel, likethe pump system of Fig. 4. However, thepump system of this modificationdifiers from that disclosed in Fig. 4 in the arrangement of the vaporbox and the diffuser jet manifold whereby additional vacuum insulationprevents leakage of heat between these parts. Furthermore, the diffuserjet manifold differs from corresponding manifold illustrated in Fig. 4in that there is here provided selective zonal cooling of the liquid andair type. The parts of Fig. 5 which are of the same construction asthose in Fig. 4 are identified by the same reference characters.

In this modified parallel-connected pump system, there is also includeda boiler 60 having suitable means for heating an organic actuating fluidcontained therein. This boiler communicates through the conduit GI withthe top of the cylindrical vapor box I05. The bottom of this vapor boxhas openings therein in which male jets are mounted to extend downward.The vapor box is completely enclosed within the cylindrical diffuser jetmanifold I06, also, preferbox. In this novel arrangement, the cover I08of the diffuser jet manifold has a central opening therein ofsubstantially larger diameter than the downward extension of the conduit6| which passes concentrically therethrough. Since the top of themanifold must be sealed, a cylindrical sleeve I09 mounted concentricallywith respect to the conduit SI has its lower edge welded to the marginof the cover plate at its central opening. The upper edge of the sleeveI09 is welded to the outer edge of an annular plate IIO, the inner edgeof which is welded to the conduit 6| which passes therethrough. By wayof example. in actual construction, the cover plate I08 may be one-halfan inch thick, the sleeve I09 onesixteenth of an inch thick and theannular plate H0 may be one-quarter of an inch thick. It will be notedthat the fiat cover and the flat plate are relatively thick for strengthwhile the sleeve which obtains its strength mainly by reason of itsshape and mounting, is relatively thin to offer an extremely poor heatconducting path between the conduit GI and the manifold walls.

Each male jet I5 opens into a diffuser jet II, while the upper portionsof these difluser jets project in sealed relation through the bottomwall of the diffuser jet manifold where they are enclosed by a fluidcooling chamber I I2. This cooling chamber is defined by the bottom andby a portion of the side wall of the diffuser jet manifold as well as bya perforated plate II3, having its periphery welded to the side wall ofthe manifold. The upper edges of the diffuser jets are sealed in theperforations in the plate I I3. Portions of a pipe I I4 communicatingwith this cooling chamber are included in a liquid circulation systemwhereby the upper portion of each diffuser jet extending approximatelyto its restricted region may be liquid cooled to any desiredtemperature. The portion of the diffuser jets extending below thedifluser manifold may be cooled by circulating air thereabout.

In this form of the invention, the lower ends of the difiuser jets openinto the reservoir 85. The left-hand portions of this reservoir isprovided with a cooling coil whereby a substantial portion of theactuating vapor is condensed while the remainder thereof proceeds to thecold condenser, as previously described in connection with the system ofFig. 4.

This last described modification operates with a high degree ofefliciency throughout the desired vacuum range and with a minimum ofheat losses.

The modified form of the invention illustrated in the diagram of Fig. 6,comprises a series-parallel connected multi-unit pump system in whichthree of the parallel-connected pumps as disclosed in Figs. 4 and 5 havesubstituted for the units A, B and C in the arrangement of Fig. 3. Itshould be pointed out that the number of male and diffuser jets in eachunit A, B and C progressively decreases from the fine vacuum end of thesystem to the forevacuum end thereof. The operation of this pump systemwill be substantially similar to that disclosed in Fig. 3.

The expression stable organic liquid as herein used, means a liquidwhich does not substantially change its chemical structure or physicalcharacteristics, other than color, over relatively prolonged periods ofuse even when subjected to the rigorous conditions encountered as a highboiling and highly accelerated actuating medium for a jet.

The present invention thus provides for the use of high-velocityelectors and high-boiling organic fluid so chosen and designed that thedecomposition ordinarily associated with high-boiling organic liquids isavoided while the high working efficiency equal to the well-known Carnotcycle, hitherto unobtainable with organic fluids, is in factsubstantially realized. This invention includes the provision of fluids,ejector and diffuser jets with entrainment ratios in excess of :1 andapproaching substantially 5: and 10:1 thus realizing from 150% of thework available according to the second law of thermodynamics. Therelation between the existing art and the present invention will best beappreciated from the following example. With Burchs invention of theoil-operated condensation pump, speeds of the order of 100 liters persecond and pressures of 10" mm. were readily available. A large" Burchcondensation pump would thus compress onetwenty-thousandth of an inch ofair per minute. That condensation pump employed a shallow pool oforganic liquid in a carefully constructedboiler in which everyprecaution was taken not to overheat the oil. A small fraction'of aliter of oil and a few hundred watts input of electricity furnished thepower and working fluid. According to the present invention, it iscontemplated to employ substantially commercial boiler practice,utilizing a boiler of 1 to 1000 H. P. capacity filled with the properlyselected fluids, piping the vapor of said fluids in large pipes,according to advanced power house practice, around many floors of alarge factory, to the multiple jet as-- semblies described herein andreturning the c"n densate by pipe line and high power mechanical pump tothe boiler. It is contemplated that a 500 H. P. installation willentrain over 2000 lbs.

of water vapor at 1 mm. pressure per minute thus bringing the technologyof a high vacuum oil pump to industrial use on a. scale never heretoforecontemplated.

What we claim is:

1. The method of producing vacuums to extremely low pressures whichmethod comprises heating a source of relatively stable organic liquid toconvert it into its vapor phase, accelerating the molecules of saidvapor, and causing said accelerated molecules to issue as a jet inaspirating relation to an opening communicating with the space to beevacuated, the speed of said issuing molecules being greater than theirrandom velocity.

2. The method of producing any degree of vac uum from 60 mm. to .001 mm.which method comprises heating to a temperature in the range from 160 to250 C., a relatively stable organic liquid, having a vapor pressure at atemperature in said range of approximately 2 to 70 cm. of mercury toconvert it into its vapor phase, accelerating the molecules of saidvapor, and causing said accelerated molecules to issue as a jet inaspirating relation to an opening communicating with the space to beevacuated.

3. The method of producing vacuums to extremely low pressures whichmethod comprises heating a source of relatively stable organic liquid toconvert it into its vapor phase, causing said vapor to issue as a jetinto a restricted passageway communicating with the space to beevacuated, the velocity of the molecules of vapor issuing as said jetbeing greater than their random velocity, and selectively coolingdilferent zones about said passageway whereby there is a substantialreduction in the tendency of the vapor molecules comprising said jet todeviate from the principal direction of movement of the jet.

4. The method of producing vacuums to extremely low pressures insuccessive stages which comprises providing highly accelerated jets ofvapor, generated from relatively stable organic liquids, at successivepoints along and in aspirating relation to the stream of gas or vaporbeing evacuated, and condensing said Organic vapors to their liquidphases, said liquids having successively lower boiling points from thefine vacuum portion of the stream to the fore vacuum portion thereof.

5. A vacuum pump system comprising a plurality of ejector unitsconnected together and operating jointly to produce low pressure, eachunit including a male jet and a diffuser jet arranged in aspiratingrelation, and fluid actuating means for said units, including a fluidderived by fractional distillation of petroleum, said fluid having aboiling point of 200 to 250 C. at pressures of 2 to 12 centimeters ofmercury.

6. A vacuum pump system comprising a plurality of ejector unitsconnected to operate in parallel relation, each unit including a malejet and a diffuser jet arranged in aspirating relation, and fluidactuating means for said units, said means including an organic fluidhaving a vapor pressure less than 5 mm, of mercury absolute pressure atthe temperature of one of said diffuser jets.

7. A vacuum pump system comprising a plurality of ejector unit connectedto operate in series-parallel relation, each unit including a male jetand a diffuser jet arranged in cooperative relation, and fluid actuatingmeans for said units, said means including at least one organic fluidhaving a vapor pressure less than 5 mm. of mercury absolute pressure atth temperature of one of said diffuser jets.

8. A vacuum pump system comprising a plurality of ejector pump unitsconnected in series, each unit including a male jet, a diffuser jet intoone end of which said male jet opens, a chamber sealing the adjacentends of said jets from the atmosphere but communicating with space to beevacuated, a boiler communicating with said male jet, an actuating fluidfor each boiler, said diffuser jet also communicating with other spacesuch as the chamber of a succeeding pump in the series, the actuatingfluids in said boilers increasing in vapor pressures from the finevacuum end of the pump system to the fore-vacuum end thereof.

9. A vacuum pump system comprising a plurality of ejector pump unitsconnected in series, each unit including a male jet, a diffuser jet intoone end of which said male jet opens, a chamber sealing the adjacentends of said jets from the atmosphere but communicating with space to beevacuated, a boiler communicating with said male jet, an actuating fluidfor each boiler, said diffuser jet also communicating with other spacesuch as the chamber of a succeeding pump in the series, the actuatingfluids in said boilers being hydrocarbons increasing in vapor pressuresfrom the fine vacuum end of the pump system to the fore-vacuum endthereof.

10. A vacuum pump system comprising aplurality of ejector pump unitsconnected in series, each unit including a male jet, a diffuser jet intoone end of which said male jet opens, a chamber sealing the adjacent ndsof said jets from the atmosphere but communicating with space to beevacuated, a boiler communicating with said male jet, an actuating fluidfor each boiler, said diffuser jet also communicating with other spacesuch as the chamber of a succeeding pump in the series, the actuatingfluids in said boilers being fractions derived by the distillation ofpetroleum, the fractions in said boilers having successively lowerboiling points from the fine vacuum end of the pump system to theforevacuum end thereof.

11. A vacuum pump system comprising a plurality of ejector pump unitsconnected in series, each unit including a male jet, a diffuser jet intoone end of which said male jet opens, a chamber sealing the adjacentends of said jets from the atmosphere but communicating with space to beevacuated, a boiler communicating with said male jet, an actuating fluidfor each boiler, said diffuser jet communicating with other space suchas the chamber of a succeeding pump in the series, said actuating fluidscomprising fractions distilled from petroleum and having boiling pointsin the range from 250 C. at a pressure of 2 cm., to C. at a pressure of20 cm.

12. A vacuum pump system comprising a plurality of ejector pump unitsconnected in series, each unit including a male jet, a diffuser jet intoone end of which said male jet opens, a chamber sealing the adjacentends of said jets from the atmosphere but communicating with space to beevacuated, a boiler communicating with said male jet, an actuating fluidfor each boiler, said diffuser jet also communicating with other spacesuch as the chamber of a succeeding pump in the series, said actuatingfluids comprising fractions distilled from petroleum and having boilingpoints in the range from 250 C. at a pressure of 2 cm. to 1 0" C. at apressure of 20 cm., the fraction in at least one of said vacuum pumpunits having a vapor pressure less than 5 mm. of mercury absolutepressure at the temperature of the diffuser jet of said last mentionedunit.

13. In a vacuum pump system, a boiler adapted to vaporize an actuatingfluid contained therein, a vapor box into which said boiler dischargesvapor, male jets communicating with said boxand projecting outwardtherefrom, a diffuser jet manifold in which said Vapor box is mounted inspaced relation to the bottom and side walls of said manifold wherebythermal leakage from said box to said manifold is greatly reduced, anddiffuser jets, each diffuser jet having one end thereof communicatingwith said manifold in alined cooperative relation with a male jet.

14. In a vacuum pump system, a boiler adapted to vaporize an actuatingfluid contained therein, a vapor box into which said boiler dischargesvapor, male jets communicating with said box and projecting outwardtherefrom, a diffuser jet manifold in which said vapor box is mounted inspaced relation to the top, bottom and side walls of said manifoldwhereby said box is thermally insulated from said manifold and diffuserjets. each diffuser jet having one end thereof communicating with saidmanifold in alined cooperative relation with a male jet.

15. In a vacuum pump system, a boiler adapted to vaporize an actuatingfluid contained therein. a vapor box into which said boiler dischargesvapor, male jets mounted in air tight relation in openings in the bottomof said box with the upper ends of said male jets projecting above theupper surface of said bottom, a diffuser jet into which each male jetopens, a diffuser manifold providing a sealed chamber enclosing thelower end of said male jets and the upper end of said diffuser jets, aconduit communicating with said manifold and with the space to beevacuated, and means for discharging condensate which forms on thementioned surface of said vapor box.

16. An ejector pump unit comprising a male jet, a source of actuatingorganic vapor supplied to said jet, a diffuser jet of the Venturi typeinto which said male jet opens, a chamber enclosing the adjacent ends ofsaid jets, an inlet pipe for gas to be evacuated, opening into saidchamber in aspirating relation to adjacent ends of said jets, condensingmeans with which said diffuser jet communicates, and means for applyingliquid cooling to the diffuser jet from the mentioned end thereof tosubstantially its narrowest portion.

17. An ejector pump unit comprising a male jet, a source of actuatingorganic vapor supplied to said jet, a diffuser jet of the Venturi typeinto which said male jet opens, a chamber enclosing the adjacent ends ofsaid jets, an inlet pipe for gas to be evacuated opening into saidchamber in aspirating relation to adjacent ends of said jets. condensingmeans with which said diffuser jet communicates, and means forselectively cooling various zones along said diffuser jet by applyingthereto liquids at different predetermined temperatures.

18. The method of producing vacuums to extremely low pressures insuccessive stages which comprises providing highly accelerated jets ofvapor. generated from relatively stable organic liquids, at successivepoints along and in aspirating relation to the stream of gas or vaporbeing evacuated, the pressure of the vapor at one of said jets being inexcess of two cm. of mercury and condensing said organic vapors to theirliquid phases, said liquids having successively lower boiling pointsfrom the fine vacuum portion of the stream to the fore vacuum portionthereof.

19. The method of evacuating a receptacle which comprises heating to atemperature in t e range of approximately 160 to 250 C., a relativelystable organic liquid having a vapor pressure at a temperature of 160 to250 C. of about 2 to '70 cm. of mercury, to convert the stable organicliquid into its vapor phase causing said vapor to pass through anexpansion nozzle whereby it becomes accelerated to exceedingly highvelocity, and entraining gases from the receptacle to be evacuated inthe high velocity jet of stable organic vapor thus formed.

20. The method of evacuating a receptacle which comprises heating to atemperature in the range of approximately to 250 C., a relatively stableorganic liquid having a vapor pressure at a temperature in saidtemperature range of about 2 to 70 cm. of mercury, to convert the stableorganic liquid into its vapor phase, causing said vapor to pass throughan expansion nozzle whereby it becomes accelerated to a velocityexceeding the random velocity of the majority of the molecules of saidvapor, and entraining gases from the receptacle to be evacuated in thehigh velocity jet of said stable organic vapor thus formed.

21. An ejector pump unit comprising a male jet, a source of relativelystable actuating organic vapor supplied to said jet, a diffuser jet ofthe Venturi type into which said male jet opens, a chamber enclosing theadjacent ends of said jets, an inlet pipe for gas to be evacuated,opening into said chamber in aspirating relation to adjacent ends ofsaid jets, condensing means with which said diffuser jet communicates,and means for applying cooling fluid to the diffuser jet from thementioned end thereof to substantially its narrowest portion.

22. An ejector pump unit comprising a male jet, a source of relativelystable actuating organic vapor supplied to said jet, a diffuser jet ofthe Venturi type into which said male jet opens, a chamber enclosing theadjacent ends of said jets, an inlet pipe for gas to be evacuatedopening into said chamber in aspirating relation to adjacent ends ofsaid jets, condensing means with which said diffuser jet communicates,and means for selectively cooling various zones along said diffuser jetby applying thereto fluids at different predetermined temperatures.

23. An ejector pump unit comprising a boiler a relatively stable organicliquid contained in said boiler to be vaporized thereby, said liquidhaving a vapor pressure at a temperature in the range from 160 to 250 C.of about 2 to '70 cm. of mercury, a male jet communicating with saidboiler, a diffuser jet of the Venturi type into which said male jetopens, a chamber enclosing the adjacent ends of said jets, an inlet pipefor gas to be evacuated, opening into said chamber in aspiratingrelation to the adjacent ends of said jets, condensing means with whichsaid diffuser jet communicates, and means for applying fluid cooling tothe diffuser jet from the mentioned end thereof to substantially itsnarrowest portion.

24. An ejector pump unit comprising a boiler a relatively stable organicliquid contained in said boiler to be vaporized thereby, said liquidhaving a boiling point higher than that of water, a male jetcommunicating with said boiler, a diffuser jet of the Venturi type intowhich said male jet opens, a chamber enclosing the adjacent ends of saidjets, an inlet pipe for gas to be evacuated opening into said chamber inaspirating relation to the adjacent ends of said jets, condensing meanswith which said diffuser jet communicates, and means for selectivelycooling various zones along said diffuser jet by applying thereto fluidsat different predetermined temperatures.

25. An ejector pump unit comprising a boiler a relatively stable organicliquid contained in said boiler to be vaporized, said liquid having avapor pressure at a temperature in the range from 160 to 250 C. of about2 to 70 .cm. of mercury, a male jet communicating with said boiler, adiffuser jet of the Venturi type into which said male jet opens, achamber enclosing the adjacent ends of said jets, condensing means withwhich said diffuser Jet communicates, and means for selectively coolingvarious zones along said diffuser jet by applying thereto fluids atdifferent predetermined temperatures.

KENNEIH C. D. I-IICKMAN. GEORGE A. KUIPERS.

